CHICAGO FIRE is celebrating its 150th episode with the Wednesday, February 6 hour, “The Plunge”—but the milestone nearly slipped by showrunner Derek Haas.

“We didn’t make any nods or plans,” he acknowledges. “It was so funny, because when you’re at this point in the season, you’re just flying by the seat of your pants in certain ways: there’s a script coming in, you have this meeting, you have that meeting. All day long stuff is happening, things are being thrown at you. You’re seeing edits of one episode, you’re rewriting another one.”

But then “we had the first meeting for the kickoff of 7×13, which is the 150th,” he continues. “At the production meeting and someone at the beginning was like, ‘This is our 150th episode!’ And I was like, ‘Oh, s—t, I forgot!’”